[PATCH 1/2] drivers: pci: do not disregard parent resources starting at 0x0

[Ard Biesheuvel]

On 11 April 2017 at 17:33, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> Commit f44116ae8818 ("PCI: Remove pci_find_parent_resource() use for
> allocation") updated the logic that iterates over all bus resources
> and compares them to a given resource, in order to decide whether one
> is the parent of the latter.
>
> This change inadvertently causes pci_find_parent_resource() to disregard
> resources starting at address 0x0, resulting in an error such as the one
> below on ARM systems whose I/O window starts at 0x0.
>
> pci_bus 0000:00: root bus resource [mem 0x10000000-0x3efeffff window]
> pci_bus 0000:00: root bus resource [io  0x0000-0xffff window]
> pci_bus 0000:00: root bus resource [mem 0x8000000000-0xffffffffff window]
> pci_bus 0000:00: root bus resource [bus 00-0f]
> pci 0000:00:01.0: PCI bridge to [bus 01]
> pci 0000:00:02.0: PCI bridge to [bus 02]
> pci 0000:00:03.0: PCI bridge to [bus 03]
> pci 0000:00:03.0: can't claim BAR 13 [io  0x0000-0x0fff]: no compatible bridge window
> pci 0000:03:01.0: can't claim BAR 0 [io  0x0000-0x001f]: no compatible bridge window
>
> While this never happens on x86, it is perfectly legal in general for a
> PCI MMIO or IO window to start at address 0x0, and it was supported in
> the code before commit f44116ae8818.
>
> So let's drop the test for res->start != 0; resource_contains() already
> checks whether [start, end) completely covers the resource, and so it
> should be redundant.
>
> Fixes: f44116ae8818 ("PCI: Remove pci_find_parent_resource() use for allocation")
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  drivers/pci/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7904d02ffdb9..53a41b1f7ef7 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -454,7 +454,7 @@ struct resource *pci_find_parent_resource(const struct pci_dev *dev,
>         pci_bus_for_each_resource(bus, r, i) {
>                 if (!r)
>                         continue;
> -               if (res->start && resource_contains(r, res)) {
> +               if (resource_contains(r, res)) {
>
>                         /*
>                          * If the window is prefetchable but the BAR is

Actually, I managed to confuse myself a bit here: $SUBJECT is
inaccurate, given that it is not the parent resource being disregarded
if it starts at 0x0 but the containee.